Wheelchair lift

ABSTRACT

A wheelchair lift having a logic module which provides several interlocks that promote proper operation is described. The logic module may be programmed to enable efficient user interface and to compensate for variations in lift operation parameters. In one embodiment, the wheelchair lift has an arm geometry which requires a lower peak force for operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 12/105,239, filed Apr. 17, 2008, now allowed which is adivisional application of U.S. patent application Ser. No. 11/387,094,filed Mar. 21, 2006, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/954,697, filed Sep. 29, 2004, entitled“Wheelchair Lift”, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/251,433 filed Sep. 20, 2002, entitled“Wheelchair Lift Device”, now U.S. Pat. No. 6,705,824, which is acontinuation of U.S. patent application Ser. No. 09/675,318 filed onSep. 29, 2000, entitled “Wheelchair Lift Device”, now U.S. Pat. No.6,461,097, each of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention is directed to a wheelchair lift. Morespecifically, the present invention is directed to a wheelchair liftwith interlocks that promote proper operation. The present invention isalso directed towards a wheelchair lift which requires a lower peakforce for operation.

2. State of the Art

Wheelchair lifts raise and lower a wheelchair and/or passenger to andfrom vehicles. wheelchair lifts are typically mounted in a doorway of avehicle with a lift mechanism and have a platform that raises and lowersthe wheelchair and/or passenger between the ground and the vehicle. Acommon wheelchair lift design uses a mounting structure comprising aparallelogram design having two sets of lift arms arranged in aparallelogram or near-parallelogram arrangement on either side of theplatform. Other designs may include mounting structures having slidingarrangements such as where the platform is horizontally stowed adjacentto the vehicle bed and slid-out to a raising and lowering position.

Wheelchair lifts may use hydraulic actuators to provide the liftingforce to move the platform. In certain situations, the use of electricactuators may provide certain features which are desirable to wheelchairlifts. For example, electric actuators may provide variable speedcontrol. However, an electric actuator of a given force rating will costmore than a hydraulic actuator of the same force rating.

What is needed is a wheelchair lift with interlocks that promote properoperation. What is also needed is a wheelchair lift which requires alower peak force for operation, to permit the practical use of electricactuators.

SUMMARY

The present invention overcomes the problems of the prior art byproviding a wheelchair lift having a logic module that provides severalinterlocks to promote proper and safe operation. The logic module mayalso be programmed to enable efficient user interface and to compensatefor variations in lift operation parameters.

Other and further features and advantages of the present invention willbe apparent from the following descriptions of the various embodimentswhen read in conjunction with the accompanying drawings. It will beunderstood by one of ordinary skill in the art that the followingembodiments are provided for illustrative and exemplary purposes only,and that numerous combinations of the elements of the variousembodiments of the present invention are possible.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which illustrate what is currently considered to be apreferred embodiment for carrying out the invention:

FIG. 1A shows one embodiment of a wheelchair lift in accordance with thepresent invention.

FIG. 1B-1F show the wheelchair lift in a ground, intermediate, floorlevel, partially stowed, and fully stowed positions.

FIG. 2A shows one embodiment of a remote control pendant that may beused with the wheelchair lift.

FIG. 2B shows a block diagram of controller features according to oneembodiment of the present invention.

FIGS. 3A-3B show a prior art arm geometry for a wheelchair lift.

FIGS. 3C-3D show one embodiment of an arm geometry in accordance withthe present invention.

FIG. 3E shows a graph of actuator force required for a prior art armgeometry and an arm geometry in accordance with the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1A shows one embodiment of a wheelchair lift 100 in accordance withthe present invention. Wheelchair lift 100 includes a mounting structurecomprising an upper arm 114 and a lower arm 115 coupled to a frame 117and a vertical arm 116. The points where upper arm 114 and lower arm 115couple to frame 117 and vertical arm 116 may form the points of aparallelogram or a near-parallelogram. A lift actuator 118 is coupled tothe point where upper arm 114 couples to vertical arm 116 and to thepoint where lower arm 115 couples to frame 117. Frame 117 is designed tobe coupled to a vehicle, and may include a threshold plate 130.

Wheelchair lift 100 also includes a platform 111 coupled to vertical arm116. Platform 111 is kept in a substantially level position by aplatform stop 129 (FIG. 1B) which rests against vertical arm 116. Aninboard roll stop 126 and an outboard roll stop 119 are coupled toplatform 111. A stow linkage is also coupled to platform 111, the stowlinkage having an upper stow arm 140, a lower stow arm 141, and a roller122. An inboard roll stop actuator 128 is coupled to inboard roll stop126 and lower stow arm 141. A handrail 112 is coupled to upper section141 of the stow linkage. A restraint belt 127 is attached to handrail112. An outboard roll stop linkage 120 is coupled to outboard roll stop119.

A logic module 200 provides several interlocks that promote the properoperation of wheelchair lift 100. Logic module 200 is described ingreater detail below. A visual alarm 132 provides a visual alert whenwheelchair lift 100 is in use, and/or when a specific event occurs suchas a mechanical or safety related condition preventing operation ofwheelchair lift 100 (e.g., weight is detected on threshold plate 130).In a preferred embodiment, two visual alarms 132 are coupled to frame117, or otherwise coupled directly to wheelchair lift 100. Audio alarmssuch as a siren or buzzer may also be included to provide audible alertsthat wheelchair lift 100 is in use, or if there is a conditionpreventing wheelchair lift 100 from being operated.

In another embodiment, audio alarms maybe in the form of voicenotifications or commands, which may be used to notify a lift operatoror passenger of a specific condition or to give instruction to take aresponsive action. Such voice-based alarms may be especially desirable,by way of example, when the operator's view of a portion of the lift isobstructed, or when a passenger is sight impaired and requires verbalnotifications to be aware of lift events. Non-limiting examples ofspecific verbal alarms may include notifying a passenger when to enterand exit the platform, that it is safe for the operator to proceed withraising or lowering the lift, or that some specific part of the liftrequires attention before operation may take place.

A platform light 134 attached to vertical arm 116 illuminates platform111 when wheelchair lift 100 is used in poor light conditions. In apreferred embodiment, two platform lights 134 are connected to eachvertical arm 116, or otherwise coupled directly to wheelchair lift 100.

FIG. 1B shows wheelchair lift 100 in a ground position. Platform 111 isnear or at ground level. Outboard roll stop 119 is lowered when outboardroll stop linkage 120 contacts the ground, thus allowing the passengerto board platform 111. Inboard roll stop 126 is raised and prevents thepassenger from traveling off platform 111.

FIG. 1C shows wheelchair lift 100 in an intermediate position after ithas begun to lift from the ground position. Outboard roll stop 119 israised as outboard roll stop linkage 120 lifts off the ground and nolonger contacts the ground, thus preventing the passenger from travelingoff platform 111. Inboard roll stop 126 is still raised.

FIG. 1D shows wheelchair lift 100 in a floor level position. Platform111 is at the level of the vehicle. Inboard roll stop actuator 128lowers inboard roll stop 126 and allows the passenger to board thevehicle. Outboard roll stop 119 is still raised.

FIG. 1E shows wheelchair lift 100 as it is folding into a stowedposition. Lift actuator 118 continues to raise upper arm 114 and lowerarm 115. After platform 111 lifts a small distance, roller 122 begins topush against lower arm 115, and upper stow arm 140 (see FIG. 1A) andlower stow arm 141 straighten out and begin to raise platform 111 into astowed position. Handrails 112 also begin to raise into a stowedposition.

FIG. 1F shows wheelchair lift 100 in the fully stowed position. Platform111 is now in an upright position. Hooks or latches may prevent platform111 from shaking or rattling while in the stowed position.

As mentioned above, logic module 200 provides several interlocks thatpromote the proper operation of wheelchair lift 100. Logic module 200 iscapable of receiving feedback from various sensors located throughoutwheelchair lift 100 and controlling the operation of wheelchair lift 100accordingly. Logic module 200 is connected to sensors which detect thepositions of platform 111, upper arm 114, lower arm 115, inboard rollstop 126, inboard roll stop actuator 128, outboard roll stop 119 andthreshold pressure plate 130, as well as whether restraint belt 127 isfastened. These sensors may include ammeters, voltmeters, limitswitches, weight sensors, optical sensors, ultrasound sensors, pressuremats, pressure switches, pressure transducers, linear encoding devicessuch as variable resistors, and any other suitable sensors. Logic module200 includes a microprocessor and software, and uses data from thesesensors to control lift actuator 118 and inboard roll stop actuator 128.Logic module 200 may also detect pressure levels, voltage levels, faultyconnections or other conditions that are relevant to the operation oflift components such as lift actuator 118 and inboard roll stop actuator128.

FIG. 2A shows one embodiment of a control pendant 205 in accordance withthe present invention. Control pendant 205 is connected to logic module200, and includes a user interface comprising buttons 240, visualdisplay 260 and keypad 270. While the various elements of the userinterface are depicted as being located on control pendant 205, itshould be understood that one or more of buttons 240, visual display 260and keypad 270 may be located directly on logic module 200 or at anyother location on wheelchair lift 100. It should further be understoodthat the number of buttons 240 and keys on keypad 270 are onlyexemplary, and any number of buttons or keys could be used.

As illustrated in FIG. 2A, control pendant 205 provides four functionswhich allow a user to operate wheelchair lift 100: UP, FOLD, UNFOLD, andDOWN. UP raises wheelchair lift 100 from the ground position to thefloor level position. FOLD stows wheelchair lift 100 from the floorlevel position into the stowed position. UNFOLD unstows wheelchair lift100 from the stowed position to the floor level position. DOWN lowerswheelchair lift from the floor level position to the ground position.Logic module 200 allows only the appropriate commands to be performed,depending on the position of wheelchair lift 100. For example, in theground position, only the UP command is available. Below the floor levelposition, only the UP and DOWN commands are available. In the floorlevel position, only the DOWN and FOLD commands are available. In thestowed position, only the UNFOLD command is available. The availablecommand choices for a given position may be indicated by the userinterface, for example, by illuminated buttons 240. Logic module 200 maystop wheelchair lift 100 if more than one button is pressed at a time oncontrol pendant 205.

Logic module 200 is capable of sending an interlock signal to thevehicle which is capable of interacting with the vehicle to preventforward and rearward movement of the vehicle when wheelchair lift 100 isnot in the stowed position. Logic module 200 is also capable ofpreventing unstowing and/or operation of wheelchair lift 100 unless aninterlock signal is received from the vehicle, indicating, for example,that the vehicle transmission is in the park position and the vehicleparking brake has been set. Logic module 200 is also capable of stoppingwheelchair lift 100 if: wheelchair lift 100 is overloaded, platform 111is occupied when a FOLD command is received, resistance is encounteredwhen wheelchair lift 100 is being stowed, outboard roll stop 119 islowered when platform 111 is more than three inches above the ground,restraint belt 127 is not fastened, and threshold plate 130 is occupiedwhen platform 111 is below the floor level position.

Logic module 200 raises and lowers inboard roll stop 126 at theappropriate points during operation of wheelchair lift 100. Beforeplatform 111 is lowered from the floor level position, logic module 200raises inboard roll stop 126. After platform 111 is raised to the floorlevel position, logic module lowers inboard roll stop 126. Logic module200 will check the position of inboard roll stop 126 or inboard rollstop actuator 128 and raise inboard roll stop 126 if necessary beforemoving platform 111, regardless of the position of platform 111. Thisprevents inboard roll stop 126 from damaging the vehicle when inboardroll stop 126 is in a partially lowered position after repairs or anyother reason while platform 111 is below the floor level position.

As shown in the embodiment illustrated by FIGS. 1B and 1C, outboard rollstop 119 may raise and lower without an actuator. In this case, logicmodule 200 may be connected to a separate ground sensor which indicateswhether platform 111 is at or near ground level, such as by monitoringthe position of outboard roll stop linkage 120, or by some otherstructure associated with platform 111 that is positioned to contact theground. Logic module 200 is thus capable of stopping platform 111 ifoutboard roll stop 119 is lowered when platform 111 is greater than, forexample, three inches from the ground. In another embodiment, logicmodule 200 may be programmed to stop further lowering either immediatelyor a predetermined time after the ground sensor indicates contact withthe ground. This feature prevents platform 111 from coming to rest in atilted or partially folded orientation when the end of platform 111including the ground sensor contacts an uneven surface, such as a curb,before the other end of platform 111 has been fully lowered to theground.

Logic module 200 is capable of preventing wheelchair lift 100 from beingstowed when platform 111 is still occupied. As can be seen in FIG. 1D,roller 122 does not yet contact lower arm 115 in the floor levelposition. A small gap is present between roller 122 and lower arm 115 inthe floor level position. When a FOLD command is received, this smallgap allows platform 111 to remain substantially level during the initialphase of the stowing operation. During this initial phase of the stowingoperation, platform 111 is lifted through a small distance of, forexample, one or two inches. This small lifting motion allows logicmodule 200 to detect weight on platform 111. In one embodiment, logicmodule 200 detects whether a pressure switch coupled to lift actuator118 is triggered during this small lifting motion. In anotherembodiment, logic module 200 detects the amperage required by liftactuator 118 to perform this small lifting motion. If the pressureswitch is triggered or an out-of-range amperage is detected, logicmodule 200 will stop platform 111. The amount of weight on platform 111necessary to prevent a stowing operation may be set, for example, to 50pounds. Because of the small initial lifting motion, the position of aweight on platform 111 does not affect this interlock. After a stowingoperation is stopped because of a weight on platform 111, logic module200 may automatically return platform 111 to the floor level position,or require the user to push the DOWN button and return platform 111 tothe floor level position. This maintains the small gap between roller122 and lower arm 115, and prevents the user from overriding thisinterlock by pressing the FOLD button repeatedly.

Logic module 200 may also be capable of preventing wheelchair lift 100from being stowed when platform 111 encounters resistance due topossible jamming of the lift apparatus. According to this embodiment,logic module 200 is programmed with a maximum pressure or amperageallowed for lift actuator 118 for stowing platform 111. When a FOLDcommand is received, logic module 200 may read the pressure or amperageon lift actuator 118 while platform 111 is rotated. If logic module 200detects that the pressure or amperage required for lift actuator 118increases a predetermined level beyond the maximum (e.g. an increase inpressure of 200 PSI), logic module 200 will stop platform 111 fromrotating. Because the weight of platform 111 will be redistributed as itrotates, a higher pressure or amperage will be required when initiatingthe stowing operation than when finishing the stowing operation.Accordingly, maximum value for pressure or amperage required of liftactuator 118 may be programmed in logic module 200 as an adjustablecurve.

In a further embodiment, logic module 200 is capable of preventingwheelchair lift 100 from lifting platform 111 from the ground to thefloor level position when it is overloaded or encounters jammingresistance. As described above with respect to FIGS. 1B and 1C, logicmodule 200 may be connected to a ground sensor which indicates whetherplatform 111 is at or near ground level. When an UP command is received,lift actuator 118 begins to lift platform 111. Logic module 200 may thendetermine whether wheelchair lift 100 is overloaded by detecting if thepressure or amperage required for lift actuator 118 is above a maximumlevel. If so, logic module 200 will stop platform 111. To determinewhether jamming resistance is encountered during lifting, logic module200 may read the pressure or amperage on lift actuator 118 shortly (e.g.1 second) after the ground switch comes out of contact with the ground.Thereafter, if logic module 200 detects that the pressure or amperagerequired for lift actuator 118 increases a predetermined level beyondthe initial reading during lifting (e.g. an increase in pressure of 30PSI), logic module 200 will stop platform 111. After a lifting operationis stopped because of overloading or jamming resistance on platform 111,logic module 200 may automatically return platform 111 to the groundlevel position, or require the user to push the DOWN button and returnplatform 111 to the ground level position.

According to another embodiment, logic module 200 is capable of stoppingwheelchair lift 100 from raising or lowering platform 111 in response tothe UP or DOWN commands when restraint belt 127 is not fastened. Ifrestraint belt 127 becomes unfastened after raising and loweringoperations have already commenced, logic module 200 may optionally beprogrammed to continue the operation and activate visual alarms 132 oran audio alarm until restraint belt 127 is refastened. In an alternativeembodiment, logic module 200 may be programmed to stop wheelchair lift100 from raising or lowering platform 111 only if it detects thatplatform 111 is occupied (e.g., the sensors indicate a weight of over 50pounds is resting on platform 111).

The above described interlocks may be further optimized by programminglogic module 200 to compensate for additional factors that may affectlift operations. Depending on atmospheric conditions or the age of thewheelchair lift 100, for example, the pressure or amperage required forlift actuator 118 to perform lifting and stowing operations may changeover time. According to one embodiment, logic module 200 may adjust itsmaximum values by tracking changes in average pressure or amperagerequired to perform operations over time. The adjustment may be based onan average value for pressure or amperage of successful lift or stowingoperations only, thereby eliminating any errors that might be introducedby failed operations. As another example, the initial pressure on liftactuator 118 when carrying out the stowing operation may vary dependingon whether platform 111 arrived at the floor level position by beingraised from the ground position or being unfolded from the stowedposition. If platform 111 is unfolded and then refolded without raisingand lowering, the pressure on lift 118 may be 30 to 40 PSI higher, forexample. In order to compensate for this difference, logic module may beprogrammed to use a different maximum fold pressure based on theprevious lift operation. Logic module 200 may also be programmed tocompensate for other factors such as battery voltage level. Whendetermining whether to prevent stowage because lift 100 is occupied, forexample, a low battery voltage level may affect the sensor reading thatdetermines whether the 50 pound weight limit is being exceeded.According to a further embodiment of the present invention, logic modulemay therefore take into consideration the battery voltage level whenreading the weight sensed on platform 111.

FIG. 2B shows one embodiment of a hardware block diagram for a logicmodule. 200 in accordance with the present invention. Logic module 200includes a micro-controller 210 which receives commands 240 from theuser through pendant 205. Micro-controller 210 also receives analoginputs 220 and switch inputs 230. Micro-controller 210 may be capable ofcommunicating with another computer through an interface 212.

BATTERY VOLTS indicates the vehicle battery charge level. Logic module200 may display a low battery indicator when the vehicle battery chargelevel is below, for example, 12.4 volts. Logic module 200 may alsoprevent wheelchair lift 100 from being unstowed or lowered when thevehicle battery charge level is below, for example, 12.2 volts. PRESSUREindicates the pressure from lift actuator 118 in an embodiment wherelift actuator 118 is a hydraulic cylinder. BUS INTERLOCK is an indicatorfrom the vehicle to logic module 200 that wheelchair lift 100 can beoperated. For example, BUS INTERLOCK may indicate that the vehicletransmission is in the park setting and that the vehicle parking brakehas been set. LIFT INTERLOCK is an indicator from logic module 200 tothe vehicle that the vehicle can be operated. For example, LIFTINTERLOCK may indicate that wheelchair lift 100 is fully stowed.

STOW SWITCH indicates whether wheelchair lift 100 is in the fully stowedposition. STOW SWITCH may be a sensor that detects the position of upperarm 114 and/or lower arm 115. LOWERING SWITCH indicates whether platform111 is at or below the floor level position. LOWERING SWITCH maybe asensor that detects the position of upper arm 114 and/or lower arm 115.PRESSURE SWITCH indicates whether there is a weight on platform 111before platform 111 can be stowed. PRESSURE SWITCH may be a pressureswitch connected to lift actuator 118 and may be set, for example, to 50pounds. OUTBOARD SWITCH indicates whether outboard roll stop 119 israised. BELT SWITCH indicates whether restraint belt 127 has beenfastened. FOLDING SWITCH indicates whether platform 111 is above thefloor level position. MAT SWITCH indicates whether threshold plate 130is occupied. GROUND SWITCH indicates whether wheelchair lift 100 is inthe ground position. EXTRA SWITCH is reserved for other features orinterlocks.

RAISE will raise platform 111. If lift actuator 118 is a hydraulicactuator, logic module 200 will turn on the pump motor for lift actuator118. LOWER will lower platform 111. If lift actuator 118 is a hydraulicactuator, logic module 200 will open the hydraulic valve for liftactuator 118. FOLD will stow platform 111. If lift actuator 118 is ahydraulic actuator, logic module 200 will turn on the pump motor forlift actuator 118 in series with a resistor to provide a slower rate ofmotion. UNFOLD will unstow platform 111. If lift actuator 118 is ahydraulic actuator, logic module 200 will open the hydraulic valve forlift actuator 118. BEACON LIGHTS will turn on visual alarm 132 whilewheelchair lift 100 is in operation. AUDIO BUZZER will turn on audioalarms while wheelchair lift 100 is in operation and/or if an interlockstops wheelchair lift 100. PLATFORM LIGHTS will turn on platform lights134 while wheelchair lift 100 is at or below the floor level position.UNLATCH will unlatch hooks which hold wheelchair lift 100 in the stowedposition. ACTUATOR+ will raise inboard roll stop 126, while ACTUATOR−will lower inboard roll stop 126.

When a command associated with buttons 240 is received from the user,micro-controller 210 first looks at the state of analog inputs 220 andswitch inputs 230 to check that all conditions have been satisfied forthe particular command. Only after all the proper conditions have beensatisfied for the particular command, will micro-controller 210 send theproper output signals 250 to effect the command. For example, when an UPcommand is received from the user, micro-controller 210 will first checkthe inputs to see (1) whether BUS INTERLOCK indicates that operatewheelchair lift 100 can be operated, (2) whether BATTERY VOLTS indicatesthere is sufficient battery voltage from the vehicle battery, (3)whether OUTBOARD SWITCH indicates that outboard roll stop 119 is raisedwhen platform 111 is greater than, for example, three inches above theground, (4) whether inboard roll stop 126 is raised by sending a signalto inboard roll stop actuator 128, (5) whether BELT SWITCH indicatesthat restraint belt 127 is fastened, and (6) whether MAT SWITCHindicates that threshold plate 130 is not occupied. Only after theseconditions for an UP command are satisfied, will micro-controller 210send the suitable signals that make tip an UP command. For example, anUP command may include: (1) turning on BEACON LIGHTS, (2) turning onAUDIO BUZZER, (3) turning on PLATFORM LIGHTS, (4) sending a RAISE outputto cause lift actuators 118 to raise platform 111 to the floor levelposition, (5) sending an ACTUATOR- output to lower inboard roll stop126, and (6) turning off AUDIO BUZZER.

Logic module 200 may also be programmed to provide additional featureswhich enhance the operation of wheelchair lift 100.

According to one embodiment of the present invention, logic module 200may be programmed to adjust operation based on the types of sensors usedto provide feedback for control of wheelchair lift 100. Sensorscomprising pressure transducers, for example, may provide differentlevels of feedback to logic module 200 based on the scale (i.e. voltageoutput to pressure ratio) for the type of transducer used. Logic module200 may be programmed to receive and store the scale value for a giventransducer, and adjust operation as required. Scale value or othersensor variables may be entered into logic module 200 using keypad 270of control pendant 205, or may be entered using other inputs such as byinterface 212. Under this embodiment, different sensors may beincorporated into wheelchair lift 100 during the course of manufacturingand maintenance without affecting control of lift operation. It alsoenables logic module 200 to be recalibrated to compensate for changes insensor feedback caused by normal wear and tear during the lifetime of alift.

Where lift actuators 118 are hydraulic actuators, logic module 200 maybe programmed to run the pump motors for lift actuators 118 for a smalladditional period of time after wheelchair lift 100 is fully stowed.This has the effect of pressurizing lift actuators 118 and minimizing orpreventing rattling of wheelchair lift 100 in the stowed position. Logicmodule 200 may also be programmed to pressurize hydraulic actuators atcertain time intervals or upon certain events to keep lift actuators 118pressurized when wheelchair lift 100 is not being used. For example,logic module 200 may pressurize hydraulic actuators every time thevehicle is started, or use pressure sensor feedback to pressurizehydraulic actuators when the pressure has dropped below a certain value(e.g. below 900 PSI for lift actuators 118 when platform 111 is in thefully stowed position). According to one embodiment, it may be desirableto configure logic module 200 to pressurize hydraulic actuators onlywhen the vehicle is on in order to avoid draining the vehicle battery.

Logic module 200 may be programmed to shut off wheelchair lift 100 if anout-of-range voltage is detected, thus acting as a programmable fuse toprevent damage to wheelchair lift 100.

Logic module 200 is capable of preventing wheelchair lift 100 from beingoperated when the vehicle battery charge level has dropped too low toprevent the vehicle battery from being drained to a point where thevehicle cannot start.

Logic module 200 is capable of recording the number of lift cycles andstow cycles. The definition of a lift cycle and a stow cycles may bechanged as needed. For example, a lift cycle may be defined as one fulltrip from the ground position to the floor level position, regardless ofhow far platform 111 has actually traveled. Logic module 200 may also becapable of calculating the total amount of work performed by wheelchairlift 100, given the distance traveled by platform 111 and the weightcarried.

As discussed above, logic module 200 includes a visual display 260 fordisplaying a variety information. Visual display 260 may be an LCDdisplay or any other suitable display. Visual display 260 may assist theuser in operation of wheelchair lift 100 by providing instructions,indicating the current command being performed, indicating the currentstatus of wheelchair lift 100, highlighting conditions that must besatisfied before wheelchair lift 100 can be operated, and suggestingcertain actions such as starting the engine to recharge the battery.Logic module 200 may be programmed to include options for the languagein which to output instructions or command information to visual display260, so that users may select between, for example, Spanish and English.In one embodiment of the present invention, information on visualdisplay 260 may be accessed and responded to through the use of keypad270.

Visual display 260 may assist in the maintenance of wheelchair lift 100by displaying the number of lift cycles and stow cycles and suggestingmaintenance to be performed. According to one embodiment of the presentinvention, microcontroller 210 may be programmed to output to visualdisplay 260 alphanumeric codes that correspond to information such asnumber of cycles or total amount of work performed. The codes may thenbe used to evaluate requirements like scheduled maintenance orcompliance with warranty requirements, without having to directly reviewdata recorded in logic module 200. A single code may also be correlatedto relate to multiple aspects of the lift operational history. In thismanner, tracking and verification of lift status may be simplified.According to a further embodiment, a chart in the form of a decal, etc.may be attached to the lift to include information providinginstructions relating to the alphanumeric codes, such as to call thelift vendor for assistance.

Visual display 260 may similarly assist in diagnostics andtroubleshooting by, for example, indicating the vehicle battery chargelevel, indicating temperatures of motors or pumps, and displaying errormessages. Visual display 260 may also be used during manufacturing,assembly, and maintenance of wheelchair lift 100 to aid in adjustmentand calibration of the various components of wheelchair lift 100. Forexample, microcontroller 260 may be programmed to output to visualdisplay 260 information about the above-described pressure, amperage andvoltage compensation settings, as well as sensor information such astransducer scale.

Wheelchair lift 100 may include a battery backup system. The batterybackup system allows wheelchair lift 100 to be operated when othersources of power are not available or have failed. The battery backupsystem exists in addition to a manual backup system, which may include ahand crank, hand pump, or other manually operated devices for operatingwheelchair lift 100.

Lift actuator 118 may be a hydraulic actuator or an electrical actuator.Electrical actuators include screw drives, rack and pinion drives, andother actuators such as Electrak™ ball bearing screw drives manufacturedby Danaher Motion Linear Products, Marengo, Ill. The use of electricalactuators allow for variable speed control of the raising and loweringof wheelchair lift 100. Electrical actuators may reduce the number ofexternal sensors needed to determine the position of wheelchair lift 100by providing feedback from sensors such as integrated potentiometers oroptical sensors. The electrical characteristics of electrical actuatorsmay be used to implement interlocks. For example, an out-of-rangevoltage detected from electrical actuators while platform 111 is beinglowered may indicate that an object is obstructing platform 111 fromlowering, thus acting as an anti-crushing feature. An out-of-rangevoltage may also indicate that platform 111 has reached the ground, thusacting as an anti-jacking feature. As another example, an out-of-rangevoltage detected from electrical actuators while platform 111 is atfloor level and while stowing of platform 111 is being attempted mayindicate that platform 111 is still occupied, thus acting as an occupiedplatform interlock. Electrical actuators also allow for control of thewheelchair lift during lowering, instead of relying on the “gravitydown” operation of hydraulic actuators. Electrical actuators may alsoallow wheelchair lift 100 to be held tightly in the stowed positionwithout unstowing, rattling, or shaking. Electrical actuators alsoprovide consistent performance over temperature changes and do not leak.

FIGS. 3A-3B show a prior art arm geometry for a wheelchair lift. Theprior art geometry is a parallelogram design.

FIGS. 3C-3D show one embodiment of an arm geometry in accordance withthe present invention. Upper arm 114 and lower arm 115 couple to frame117 at two points that are farther apart than in the prior art geometry.In addition, the two points are located along a steeper angle than inthe prior art geometry.

This lift arm geometry reduces the distance between the point whereupper arm 114 couples to frame 117 and to the point where lower arm 115couples to vertical arm 116 as the lift arms are passing through ahorizontal position.

This lift arm geometry reduces the peak force needed from lift actuator118. The reduced peak force required makes this lift arm geometrysuitable for use with electrical actuators, which may not be able togenerate as much force as hydraulic actuators of comparable cost.However, hydraulic actuators may still be used and benefit similarlyfrom this lift arm geometry.

FIG. 3E shows a graph of actuator force required for the prior art armgeometry and an arm geometry in accordance with the present invention.As can be seen, the prior art arm geometry requires an actuator force ofmore than 2000 pounds when its platform has reached the floor levelposition. An arm geometry in accordance with the present inventionrequires an actuator force of less than 1200 pounds when its platformhas reached the floor level position, with the maximum force during thelifting of the platform not exceeding 1300 pounds.

Although the above examples have described wheelchair lift 100 in thecontext of carrying a wheelchair and/or a passenger, wheelchair lift 100may be used in other applications. Wheelchair lift 100 may be used inthe same or modified form to be attached to different parts of a vehicleand to carry other types of payloads. Rather than having a mountingstructure comprising a parallelogram design as illustrated, for example,wheelchair lift 100 may comprise another design such as a slidingassembly.

While the invention is described in terms of some specific examples andembodiments, it will be clear that this invention is not limited tothese specific examples and embodiments and that many changes andmodified embodiments will be obvious to those skilled in the art withoutdeparting from the true spirit and scope of the invention.

1. A wheelchair lift comprising: a frame connected to a vehicle; amounting structure coupled to the frame; at least one electric actuatoroperatively connected to the mounting structure; and a platformconnected to the mounting structure, said mounting structure and said atleast one electric actuator cooperate to move the platform into one of astowed, floor or ground position; wherein the electric actuator providesvariable speed control of the platform movement when raising or loweringthe platform.
 2. The wheelchair lift according to claim 1, wherein theelectric actuator comprises electrical characteristics which are used toimplement interlocks into the lift without requiring additional sensors.3. The wheelchair lift according to claim 2, wherein one electricalcharacteristic comprises an out-of-range amperage condition.
 4. Thewheelchair lift according to claim 3, wherein the out-of-range amperagecondition identifies an anti-crushing interlock.
 5. The wheelchair liftaccording to claim 3, wherein the out-of-range amperage conditionidentifies an anti-jacking interlock.
 6. The wheelchair lift accordingto claim 3, wherein the out-of-range amperage condition identifies aplatform occupied interlock.
 7. A wheelchair lift comprising: a frameconnected to a vehicle; a mounting structure coupled to the frame; atleast one electric actuator operatively connected to the mountingstructure, said at least one electric actuator having one or moreintegrated sensors; a platform connected to the mounting structure, saidmounting structure and said at least one electric actuator cooperate tomove the platform into one of a stowed, floor or ground position; and alogic module (200) configured to receive feedback from the one or moreintegrated sensors of the electric actuator for determining a positionof the wheelchair lift.
 8. The wheelchair lift according to claim 7,wherein the electric actuator comprises electrical characteristics whichare used to implement interlocks into the lift without requiringadditional sensors.
 9. The wheelchair lift according to claim 8, whereinone electrical characteristic comprises an out-of-range amperagecondition.
 10. The wheelchair lift according to claim 9, wherein theout-of-range amperage condition identifies an anti-crushing interlock.11. The wheelchair lift according to claim 9, wherein the out-of-rangeamperage condition identifies an anti-jacking interlock.
 12. Thewheelchair lift according to claim 9, wherein the out-of-range amperagecondition identifies a platform occupied interlock.